Display devices which have an active matrix substrate in which a switching element is provided for each pixel, such as liquid crystal display devices, have been widely used. An active matrix substrate which includes thin film transistors (hereinafter, “TFT(s)”) as the switching elements is referred to as a TFT substrate. A TFT substrate for use in a liquid crystal display device includes, for example, a glass substrate, a plurality of TFTs supported on the glass substrate, a plurality of gate wires and a plurality of source wires, and a plurality of pixel electrodes in a matrix arrangement. The plurality of gate wires are arranged so as to extend in, for example, a row direction of the display plane. The plurality of source wires are arranged so as to extend in, for example, a column direction of the display plane. The gate electrode, source electrode, and drain electrode of each TFT are electrically coupled to a gate wire, a source wire, and a pixel electrode, respectively.
Liquid crystal display devices are known which have such a configuration that pixel electrodes are arranged on an insulating film that covers TFTs, gate wires, and source wires, wherein the pixel aperture ratio is improved by adjusting the thickness and/or dielectric constant of the insulating film and reducing a parasitic capacitance formed by overlap of an edge portion of the pixel electrode with the gate wires and/or the source wires (for example, Patent Documents 1 to 4). In such a liquid crystal display device, the insulating film is typically made of an organic insulative material. This is because organic insulative materials advantageously have lower dielectric constants and/or are better for formation of a thick film than inorganic insulative materials.
However, formation of a relatively-thick insulating film leads to the following problems.
A display region which is formed by the pixels that are in a matrix arrangement on the TFT substrate is surrounded by a non-display region (which is referred to as “frame region”). In some cases, terminal portions and even a driving circuit portion are provided in the frame region in addition to a seal portion that is for adhering together two substrates (TFT substrate and counter substrate) which are arranged so as to oppose each other via a liquid crystal layer. In such a configuration, the insulating film is provided over generally the entirety of the display region but is not provided at least over the terminal portions of the frame region. Thus, over the TFT substrate, there are a region in which the insulating film is provided and a region in which the insulating film is not provided. If the insulating film is thick, a relatively-large step is formed.
Accordingly, in the process of forming a pixel electrode by patterning an electrically-conductive film deposited on the insulating film, part of the electrically-conductive film remains near the edge of the insulating film so that a short circuit can sometimes occur between wires (gate wires and/or source wires) which adjoin each other. This is attributed to the fact that the thickness of a resist mask used for patterning of the electrically-conductive film is greater on the bottom side of the step of the insulating film than on the top side so that the resist mask remains. A portion of the resist mask which is thus remaining although it should have been removed after development is referred to as “resist residue”.
Patent Documents 1 and 2 disclose that the pattern of the insulating film has a portion extending between wires in the frame region such that occurrence of a resist residue in the vicinity of the edge of the insulating film is suppressed. Patent Documents 3 and 4 suggest that the edge of the insulating film is configured so as not to have a steep slope angle such that occurrence of a resist residue in the vicinity of the edge of the insulating film is suppressed.